Even putting aside my great dislike for Scala (which I discussed on HN ad nauseam :)), I think everyone would agree that Scala has a very different philosophy from Java. Java has been designed as a "blue-collar" language, with maintenance of a large project with possibly hundreds of developers as a central guiding principle. C#, Go, Dart, Kotlin, Fantom etc., have a similar philosophy. But Scala is a different beast altogether. You can love it or hate it, but even its most enthusiastic fans would concede that it is most certainly not appropriate as a replacement for Java in some/many/most (depending on your view) circumstances.

Also, Java is extremely popular, and some of its most painful points have been addressed in Java 8. Even an arguably better language (regardless of its name) will not easily replace Java. Hey, look across the browser at JavaScript. There are arguably better languages there; are they replacing JavaScript?

If you look just at GitHub – which is greatly skewed towards new languages – you see that all other JVM languages put together make about 10% of the JVM ecosystem, with Java being the 90%. Outside of GitHub, in "the real world", the situation is even more strongly in favor of Java. I don't know if this is going to change much in the next few years.

I don't mean that you shouldn't use an alternative JVM language if it makes your work better, and there are many viable and very useful alternate JVM languages – personally, I like Clojure and Kotlin – but you can't just "replace" Java so easily. I think efforts to reform the Java ecosystem are more likely to succeed – at least in the short term – than efforts that require switching to a different JVM language.